1. Field of the Invention
This invention relates to an activated carbon based adsorbent for mercury or mercury compounds contained in liquid hydrocarbons, more particularly to activated carbon based adsorbents and methods for adsorbing and eliminating small amounts of mercury or mercury compounds (hereinafter often simplified to "mercury") contained in liquid hydrocarbons, for instance naphtha and intermediates of oil products or petrochemical products.
2. Description of the Related Art
Heretofore, alumina based catalyst carrying palladium, for instance, has been used for the hydrogenation process of reforming liquid hydrocarbons, such as naphtha. The hydrogenation reaction on the catalyst suffers if impurity mercury or mercury compounds are present in the liquid hydrocarbons.
Mercury lends to readily form amalgams with many kinds of metals. For such reason, if an apparatus constructed from aluminum based alloys is involved in such process, there is harmful risk of corrosion due to amalgamation with mercury. Accordingly there has been strong desire for progress in the elimination of mercury from such liquid hydrocarbons.
There has been reported an adsorbent for mercury, based on a porous adsorbent carrying sulfur, that eliminates mercury by chemical reaction between mercury and sulfur. Further physical adsorption involving no chemical reaction with use of a porous adsorbent such as activated carbon, zeolite, or alumina is feasible to eliminate inorganic mercury in hydrocarbons. However, this method has problems such as inferior performance in mercury elimination rate when the adsorption performance decreases at a mercury concentration less than 10 bbp.
In the art disclosed heretofore concerning the adsorbent carrying sulfur, the sulfur carrying activated carbon is, for example, prepared by mixing activated carbon with fine sulfur particles and heating such mixture at 110.degree.-400.degree. C. (Japanese patent Application laid-open No. 59 78915/1984); and can be activated carbon carrying organic sulfur compound (Japanese Patent Application laid-open No. 62-114632/1987). Therein, as the sulfur compound, the use of solid sulfur or an organic sulfur compound such as thiophene is typical. Such porous adsorbents carrying a sulfur compound have been intended mainly to eliminate mercury from gases, rather than from liquid hydrocarbons.
Further, such art does not intend to inhibit dissolution or dessorption of the sulfur carried by the adsorbents into the liquid hydrocarbon as contamination, in addition to eliminating mercury. Liquid hydrocarbons are mostly subjected to hydrogenation at the stage of intermediate product wherein the contaminant or impurity sulfur contained in such hydrocarbon would give serious damage to the catalysts for hydrogenation. Thus there are deficiencies in the known art.